CN1831383A - Piston for automatic transmission - Google Patents

Abstract

The present invention provides a piston (18) for an automatic transmission, wherein a first piston member (46) forming a cylindrical portion of the piston is formed with a plurality of axial slits (68) and A circumferential groove (51), the second piston member (48, 82) forming the bottom of the piston has radially extending engagement pawls (66, 80) fitting in said axial cutouts, engaging A ring (50) fits in said circumferential groove and is held in abutting contact with said engagement pawl fitted in said axial notch, whereby the first piston member and the second piston member are fixed to each other. At least one of the plurality of engaging claws (66, 80) of the second piston member (48, 82) cooperates with the snap ring (50) to form a gap (74, 76, 84) therebetween, which prevents the piston (18) from ) during the axial movement, the stress concentration at the position adjacent to the axial notch (68) of the circumferential groove (51) can reduce the required thickness of the snap ring (50) and make the piston compact.

Description

Pistons for automatic transmissions

This application is based on Japanese Patent Application No. 2005-066121 filed on March 9, 2005, the contents of which are incorporated herein by reference.

technical field

The present invention relates to a piston usable for pressing frictional engagement elements of a clutch or brake device provided in an automatic transmission against each other to place the clutch or brake device in its engaged state.

Background technique

A known automatic transmission includes clutches and brakes each having frictionally engaging elements in the form of a plurality of friction plates so that the automatic transmission can automatically shift gears by selectively engaging and releasing the clutches and brakes. The friction engagement elements are pressed against each other by pistons to place each clutch or brake in its engaged state. JP-9-32919A and JP-10-89380A disclose an example of a piston comprising two piston parts, namely, a first piston part forming the cylindrical portion of the piston and a second piston part forming the bottom of the piston. Two piston parts. In the pistons disclosed in these documents, the first piston member has an axial slit formed on one of its opposite axial ends, and the second piston member has an engaging portion that fits into the axial slit. Claws, and a snap ring in contact with the second piston member is fitted in a circumferential groove formed on the inner peripheral surface of the first piston member, so that the first piston member and the second piston member are fixed to each other in the piston. The circumferential grooves are formed by a plurality of arcuate grooves separated from each other by axial cuts in the circumferential direction of the first piston member.

In the piston disclosed in JP-9-32919A, the axial movement of the piston causes a load to be applied from the second piston member to the circumferential groove of the first piston member through the snap ring. Engaging pawls formed on the second piston member extend radially of the piston and can abut against the snap ring so that the load is applied from the engaging pawls to the snap ring when the piston moves axially. The snap ring fits only in the circumferential groove of the first piston member, in contact with the second piston member having engaging claws fitted in the axial cutouts of the first piston member, without any part of the snap ring remote from the engaging claws. The part of the side bearing the snap ring, the application of load by the snap ring from the second piston part to the circumferential groove of the first piston part results in a portion of the circumferential groove adjacent to the circumferential axial cutout of the first piston part produce stress concentrations. Therefore, these portions of the circumferential groove tend to deform elastically due to stress concentration.

Therefore, in order to prevent the elastic deformation of the circumferential groove of the first piston member in the piston of JP-9-32919A, the thickness of the snap ring must be sufficiently large, which undesirably leads to an increase in the size of the piston.

Contents of the invention

The present invention is accomplished based on the above-mentioned background technology. It is therefore an object of the present invention to provide a small piston for an automatic transmission comprising a first piston member forming a cylindrical portion thereof and a second piston member forming a bottom thereof, wherein the first piston member and the second piston The pieces are secured to each other by snap rings.

The above object can be achieved according to the principles of the present invention. The present invention provides a piston for an automatic transmission, comprising: a first piston member forming a cylindrical portion of the piston, and a plurality of Axial slits and a circumferential groove; forming the bottom of the piston and having a second piston member that fits in a plurality of radially extending engagement claws in the axial slits; and fits in the circumferential groove and a snap ring held in abutting contact with the engaging claws so that the first piston member and the second piston member are fixed to each other, wherein at least one of the plurality of engaging claws of the second piston member is in contact with the engaging claws. The snap rings fit together to form a gap therebetween.

In the piston of the present invention constructed as described above, at least one of the radially extending engagement claws of the second piston member held in abutting contact with the snap ring cooperates with the snap ring to form or define a gap therebetween. Due to the existence of this gap, when the force is applied to the snap ring by the second piston member when the piston moves axially, the snap ring is not engaged from the engagement claw, that is, from the peripheral portion of the second piston member corresponding to the axial notch. The ring is loaded. Therefore, the gap formed between the engaging claw and the snap ring prevents stress concentration on the portion of the circumferential groove of the first piston member adjacent to the axial cutout, so that the required thickness of the snap ring can be reduced and the piston can be compacted. .

According to a first preferred form of the invention, each of said at least one of said plurality of engaging pawls has a shoulder comprising a radially outer portion and a radially inner portion, said radially outer portion and radially inner portion being surrounded by Formed such that the radially outer portion is spaced away from the radially inner portion in the axial direction of the second piston member away from the snap ring, the shoulder cooperates with the snap ring to form the gap.

According to a second preferred form of the invention, the axially inner ends of said plurality of axial slits are defined by respective radial end faces parallel to the radial direction of said first piston member and along said The axially outer end of the first piston member axially remote from the axial notch is spaced from the circumferential groove, and the plurality of engagement pawls are formed of at least one elastically biased pawl and at least one inelastically biased pawl , wherein the at least one elastic biasing claw is inclined toward the radial end surface along the axial direction of the second piston member and each of the elastic biasing claws is in the radial direction of the corresponding one of the plurality of axial slits. end faces are held in abutting contact, said at least one non-resiliently biased pawl is not in abutting contact with a radial end face of a corresponding axial slit, each of said at least one non-resiliently biased pawl cooperates with said snap ring to define a first gap therebetween, and each of the at least one elastically biased pawl cooperates with the snap ring to define a second gap therebetween, and the size of the first gap along the axial direction of the piston is smaller than that of the first gap. The dimension of the two gaps along the axial direction of the piston.

In the second preferred form of the piston according to the present invention, each resiliently biased pawl inclined toward the radial end face of the corresponding axial notch in the axial direction of said second piston member is in abutting contact with said radial end face. is held such that the first piston member is axially biased by said respective resiliently biased pawl. The at least one resiliently biased pawl is effective to minimize relative axial rattling movement of the first and second piston members of the piston even while maintaining dimensional errors within predetermined tolerances. Inner time can also be caused by dimensional errors of the piston parts. Thus, the at least one elastically biased pawl reduces the degree of deterioration of the durability of the first piston part and of the frictionally engaging elements (friction plates) of the clutch or brake device, wherein the deterioration of durability may be due to the frictional engagement of the first piston part with the caused by unwanted abutment contact of components. Therefore, said at least one elastically biased pawl can effectively reduce the automatic frictional engagement due to the dragging phenomenon of the clutch or brake device-when the clutch or brake device does not need to be placed in its engaged state, the frictional engagement elements are pressed against each other by the piston. Transmission power loss.

The second preferred form of piston according to the invention is also due to the fact that the axial dimension of the first gap formed between the non-resiliently biased pawl and the radially outer end of the snap ring is smaller than that of the resiliently biased form formed in the second engaging pawl. The axial dimension of the second gap between the claw and the snap ring is advantageous. This dimensional relationship between the first gap and the second gap is advantageous when assembling the first piston part and the second piston part. That is, the resiliently biased and non-resiliently biased jaws may deform due to relative axial movement of the first and second piston members during assembly. Even when the elastically biased claw and the non-elastically biased claw are deformed, the non-elastically biased claw is in abutting contact with the snap ring before the elastically biased claw is in abutting contact with the snap ring. When the non-resiliently biased pawl is in abutting contact with the snap ring, further movement of the first piston member in the axial direction relative to the second piston member is prevented, thereby preventing subsequent elastic deformation of the resiliently biased pawl, thereby preventing elastic deflection. Elastic deformation of the jaws.

Although at least one engaging claw of the plurality of engaging claws (two or more engaging claws) of the second piston member needs to cooperate with the snap ring to form a gap therebetween, it is desirable that all the engaging claws cooperate with the snap ring to form a gap therebetween. Create corresponding gaps.

In the piston according to the first preferred form of the present invention, the radially outer portion and the radially inner portion of the shoulder are formed such that the radially outer portion is away from the snap ring and the radially inner portion in the axial direction of the second piston member. section separated. In this case, the thickness of the engaging jaws which partly define the gap is equal to the thickness of the remainder of the second piston member. However, the gap may also be formed between the snap ring and a portion of the engaging claw having a thickness smaller than that of other portions of the engaging claw. The shoulder engaging the jaws may also be formed by forming the second piston member by bending a flat blank or workpiece, for example by a press-forming operation, or by machining the blank or workpiece.

Each of said at least one of said plurality of engagement pawls may be constituted by a single straight portion extending radially outwardly of said second piston member and opposite to the second piston member at its proximal end. The radial curvature of the piston member is such that the distal end of the single straight portion is spaced from the proximal end axially of the second piston member away from the snap ring.

An inner end portion of the gap as viewed in the radial direction of the second piston member may be located outside an inner end surface of the first piston member in which a circumferential groove is formed. However, the inner end of the gap is preferably located on the inner side of the inner peripheral surface of the first piston member. This structure can effectively reduce the stress concentration on the circumferential portion of the circumferential groove adjacent to the axial notch. If the inner end of the gap is closer to the inner side of the inner peripheral surface of the first piston member, the surface area of the engaging claw in abutting contact with the snap ring is correspondingly reduced, so that the load applied to the snap ring from the second piston member Uneven around the circumference of the snap ring. Therefore, the inner end surface of the gap is preferably located on the inner side of the inner peripheral surface of the first piston part, but as close as possible to the inner peripheral surface of the first piston part.

Said at least one resiliently biased pawl provided in the second preferred form of piston according to the invention need not be provided in accordance with the principles of the invention. In a second preferred form, said at least one resiliently biased pawl and said at least one non-resiliently biased pawl are provided. Each resiliently biased pawl is inclined toward the radial end face of the corresponding axial cutout in the axial direction of the second piston member. That is, each elastic biasing claw includes a radially outer portion and a radially inner portion formed such that the radially outer portion is directed toward the radial end surface in the axial direction of the second piston member. and spaced from the radially inner portion away from the snap ring. The resiliently biased pawl may also have the shoulder provided in the first preferred form of the invention described above, or may consist of a single straight section as described above. Regardless of the configuration of the resiliently biased claw, a gap is formed between the resiliently biased claw and the snap ring, and the resiliently biased claw serves as at least one engaging claw provided in accordance with the principles of the present invention described above. When the amount of clearance partially defined by the engagement pawl in abutting contact with the radial end face is greater, the engagement pawl is considered to be a resiliently biased pawl. In other words, the amount of clearance defined in part by the resiliently biased jaw is greater than the amount of clearance defined in part by the non-resiliently biased jaw.

Description of drawings

By reading the following detailed description of preferred embodiments of the present invention in conjunction with the accompanying drawings, the above and other objects, features, advantages and technical and industrial significance of the present invention can be better understood, wherein:

1 is a partial front sectional view of an automatic transmission provided with a clutch device comprising a piston in the form of a radially outer piston constructed in accordance with a first embodiment of the invention;

Fig. 2 is the view taken along the direction of the arrow line A of Fig. 1;

Fig. 3 is the view taken along the direction of the arrow line B of Fig. 1;

4 is an enlarged cross-sectional view showing a first engagement claw of the piston and its vicinity;

5 is an enlarged cross-sectional view showing a resiliently biased pawl in the form of a second engagement pawl of the piston and its vicinity;

Figure 6 is an enlarged cross-sectional view corresponding to Figure 4, showing a first engaging pawl of a piston constructed in accordance with a second embodiment of the present invention;

Fig. 7 is an enlarged cross-sectional view corresponding to Fig. 4, showing a first engagement pawl of a piston constructed in accordance with a third embodiment of the present invention.

Detailed ways

Referring first to FIG. 1 , which is a front sectional view, there is shown a portion of an automatic transmission 8 having a clutch arrangement 10 including a piston in the form of a radially outer piston 18 constructed in accordance with one embodiment of the present invention.

The clutch device 10 is a double clutch structure, and includes: a clutch drum 16 supporting the first group of frictional engagement elements 12 and the second group of frictional engagement elements 14; an outward piston 18 ; and a radially inward piston 20 disposed radially inwardly of the clutch drum 16 .

The automatic transmission 8 includes a housing 24 and an input shaft 22 rotatably supported by the housing 24 at its end 22a. The input shaft 22 has a flange portion 22b at an axial position close to the end portion 22a. The flange portion 22 b extends radially outward perpendicular to the axis of the input shaft 22 . The input shaft 22 is a turbine shaft of a torque converter driven by a driving force source such as an engine of an automobile.

The clutch drum 16 is composed of a radially inner hub portion 26 and a radially outer drum portion 28 . The radially inner hub portion 26 is a substantially cylindrical member having a substantially constant outer diameter and fitted over the axially extending cylindrical portion 24 a of the housing 24 . The radially inner hub portion 26 includes a thin-walled axial end portion 26 a on the radially inner piston 20 side. The inner peripheral surface of the radially inner hub portion 26 has a tapered step portion 26b adjacent to the axial end portion 26a. The inner diameter of the tapered portion of the tapered step portion 26b increases in the radial direction of the radially inner hub portion 26 toward the thin-walled axial end portion 26a. The axial end portion 26 a has an end surface that is flush with one of the opposing surfaces of the flange portion 22 b of the input shaft 22 on the radially inner piston 20 side. The radially inner hub portion 26 and the input shaft 22 are welded to each other at the outer peripheral surface of the flange portion 22b and the inner peripheral surface of the axial end portion 26a. The flange portion 22b of the input shaft 22 and the tapered step portion 26b of the axial end portion 26a of the radially inner hub portion 26 cooperate to partially define an oil sump 30 formed radially inward of the tapered step portion 26b.

The radially outer drum portion 28 is a cylindrical member constituted by an inner cylindrical portion 28a, an outer cylindrical portion 28c, and an annular bottom portion 28b connecting respective axial ends of the inner cylindrical portion 28a and the outer cylindrical portion 28c. One axial end of the radially outer drum portion 28 is closed by an annular bottom 28b, while the other axial end is open.

The inner cylindrical portion 28a is fitted on the thin-walled axial end portion 26a of the radially inner hub portion 26, and the end face of the inner cylindrical portion 28a on the radially inner piston 20 side is flush with the corresponding end face of the axial end portion 26a . The radially inner hub portion 26 and the radially outer drum portion 28 are welded to each other at the inner peripheral surface of the inner cylindrical portion 28a and the outer peripheral surface of the axial end portion 26a. Accordingly, the radially outer drum portion 28 and the radially inner hub portion 26 rotate together with the input shaft 22 .

The annular bottom portion 28b of the radially outer drum portion 28 extends radially of the input shaft 22 based on the top, and is connected at its radially inner end to the axial end portion of the inner cylindrical portion 28a on the radially outer clutch piston 18 side. . The outer cylindrical portion 28c extends in the axial direction (rightward direction as seen in FIG. 1 ) from the radially outer end of the annular bottom portion 28b. The outer cylindrical portion 28c holds a plurality of inwardly extending friction plates 32 of the first set of frictional engagement elements 12 and a plurality of inwardly extending friction plates 38 of the second set of frictional engagement elements 14 such that the friction plates 32 are in spline engagement to a part of the inner peripheral surface of the outer cylindrical portion 28c that is closer to the axial opening end of the outer cylindrical portion 28c, and makes the friction plate 38 spline-bonded to the inner peripheral surface that is closer to the annular bottom 28b and farther away from the above-mentioned part of the axial open end. The friction plates 32 , 38 extend from the inner peripheral surface of the outer cylindrical portion 28 c in the radially inward direction of the clutch drum 16 . The first group of friction engagement elements 12 is composed of the above-mentioned inwardly extending friction plates 32 and a plurality of outwardly extending friction plates 34 arranged alternately along the axial direction of the clutch drum 16 . Likewise, the second group of friction engagement elements 14 is composed of the above-mentioned inwardly extending friction plates 38 and a plurality of outwardly extending friction plates 40 arranged alternately along the axial direction.

The outwardly extending friction plates 34 of the first set of friction engagement elements 12 are splined to an outer peripheral surface of a ring gear 36 of the automatic transmission 8 serving as a clutch hub. Outwardly extending friction plates 40 of the second set of friction engaging elements 14 are splined to an outer peripheral surface of a clutch hub 42 . The clutch driven hub 42 is fixedly fitted on its inner peripheral surface to a sun gear 44 fixedly fitted to the input shaft 22 so that the clutch driven hub 42 rotates together with the sun gear 44 .

The radially outer piston 18 is composed of the following components: a first piston member 46 arranged radially outside the outer cylindrical portion 28c of the radially outer drum portion 28 and forming the cylindrical portion of the piston 18; an annular second piston member 48, one of the opposite axial ends engaging and forming the bottom of the piston 18; The piston member 48 moves away from the snap ring 50 of the first piston member 46 . The snap ring 50 is fitted on its radially outer portion in a circumferential groove 51 formed in the inner peripheral surface of the first piston member 46 . The circumferential groove 51 is constituted by a plurality of arc-shaped grooves separated from each other in the circumferential direction of the first piston member 46 by a plurality of axial cutouts 68 (to be described later).

The inner peripheral surface of the second piston part 48 of the radially outer piston 18 is axially slidable on the radially inner hub 26 . The second piston member 48 cooperates with the annular bottom portion 28b of the radially outer drum portion 28 to define a first hydraulic chamber 52 to which working oil is supplied via an oil passage 54 formed through the radially inner hub portion 26 , The radially outer piston 18 is thereby axially movable such that the second piston member 48 moves away from the annular bottom 28 b of the radially outer drum 28 .

On the side away from the first hydraulic chamber 52 among the opposite axial sides of the second piston member 48 , there is provided a balance weight 58 whose inner peripheral surface fits on the outer peripheral surface of the radially inner hub portion 26 . The counterweight 58 cooperates with the second piston member 48 of the radially outer piston 18 to define a second hydraulic chamber 60 . A return spring 62 is disposed between the balance weight 58 and the second piston member 48 to bias the balance weight 58 and the second piston member 48 to move away from each other in opposite axial directions. The axial position of the balance weight 58 biased axially away from the radially outer piston 18 by the return spring 62 is determined by the balance weight 58 at its radially inner end and the outer peripheral surface fixed on the radially inner hub 26 The abutment contact of the snap ring 64 is determined.

The radially inner hub portion 26 has an oil passage (not shown) for communicating the second hydraulic chamber 60 and the oil sump 30 so that working oil is introduced into the second hydraulic chamber 60 through the oil passage. Therefore, the second hydraulic pressure chamber 60 functions as a cancellation chamber for canceling the centrifugal hydraulic pressure formed in the first hydraulic pressure chamber 52 . Working oil is discharged from the second hydraulic chamber 60 to the shaft of the counterweight 58 away from the second hydraulic chamber 60 through an axial groove 65 formed on the axial portion of the radially inner hub portion 26 that cooperates with the counterweight 58 . in the side space.

The first piston member 46 of the radially outer piston 18 is formed by pressing, and is composed of a cylindrical portion 46a disposed in the radial direction of the outer cylindrical portion 28c of the radially outer drum portion 28 and a pressing portion 46b. On the outside, the pressing portion 46 b is formed to extend from the axial end portion of the cylindrical portion 46 a away from the second piston member 48 . The pressing portion 46b extends substantially in the radially inward direction, and is inclined axially toward the frictional engagement elements 12 of the first group so that the radially inner end portion of the pressing portion 46b rubs against the closest frictional engagement element 12 of the first group. Sheet 32 is opposite. When the pressurized working oil is not supplied to the first hydraulic chamber 52 , a small amount of clearance remains between the radially inner end portion of the pressing portion 46 b and the above-mentioned nearest friction plate 32 . The outer cylindrical portion 28 c of the radially outer drum portion 28 has a snap ring 56 fixed to its inner peripheral surface to prevent axial movement of the first-group frictional engagement elements 12 toward the second-group frictional engagement elements 14 .

Referring now to FIG. 2 taken in the direction of the arrow line A of FIG. 1 , the second piston member 48 of the radially outer piston 18 is shown. The second piston member 48 is also formed by pressing, and has a plurality of first engaging claws 66a and a plurality of second engaging claws 66b, such as shown in FIG. The four first engaging claws 66a and the four second engaging claws 66b. The first engaging claws 66 a and the second engaging claws 66 b are alternately arranged at predetermined intervals along the circumferential direction of the second piston member 48 . These first engagement claws 66 a and second engagement claws 66 b are collectively referred to simply as engagement claws 66 .

As shown in FIG. 3 taken in the direction of the arrow line B of FIG. 1 , the cylindrical portion 46 a of the first piston member 46 has the aforementioned plurality of axial cutouts 68 . These cutouts 68 are formed in the axial end portion of the cylindrical portion 46 a where the first piston member 46 is fixed to the second piston member 48 . The notch 68 extends from the edge of the above-mentioned axial end portion of the cylindrical portion 46a in the axial direction of the first piston member 46, and is formed to penetrate through the wall thickness of the cylindrical portion 46a. The engagement claws 66 of the second piston member 48 are held in engagement with the corresponding axial slits 68 spaced apart from each other in the circumferential direction of the first piston member 46 at the same pitch as that between the engagement claws 66 . open.

Referring to the enlarged cross-sectional views of FIGS. 4 and 5 , there are shown a first engagement claw 66 a and its vicinity and a second engagement claw 66 b and its vicinity, respectively. As shown in FIG. 4 and FIG. 5, the first engagement claw 66a and the second engagement claw 66b are each bent along the axial direction of the first piston member 46 away from the snap ring 50, so that the curved first engagement claw 66a and the second engagement claw 66a The engagement pawl 66b forms respective first and second shoulders 70 , 72 on the snap ring 50 side. First and second shoulders 70 , 72 respectively cooperate with radially outer portions of snap ring 50 to define first and second gaps 74 , 76 respectively therebetween. Each shoulder 70 , 72 includes a radially inner portion and a radially outer portion formed such that the radially outer portion is away from the snap ring 50 in the axial direction of the second piston member 48 spaced from the radially inner portion. The second piston member 48 has a constant thickness in the radial direction. That is, the thickness of each engagement claw 66 is equal to the thickness of the rest of the second piston member 48 .

The bending amount of the first engaging claw 66a is smaller than that of the second engaging claw 66b, so that the dimension d1 of the first gap 74 along the axial direction of the radially outer piston 18 is smaller than the dimension d2 of the second gap 76 along the axial direction. In this arrangement, each first engagement pawl 66a is spaced apart from a radial end face 68a parallel to the radial direction of the first piston member 46 and defining the axially inner end of the respective axial notch 68 . The radial end face 68 a is spaced apart from the circumferential groove 51 in the axial direction of the first piston part 46 away from the axially outer end of the corresponding axial notch 68 . On the other hand, each second engaging claw 66b is held in abutting contact with the radial end surface 68a while biasing the first piston member 46 axially away from the snap ring 50, so that the second engaging claw 66b acts as an elastic bias. The role of claws. In this regard, the first engagement pawl 66a may be referred to as a non-resiliently biased pawl.

If all engaging pawls 66 of the second piston member 48 are first engaging pawls 66a, and there is no second engaging pawl 66b which acts as an elastic biasing pawl, then the first piston member 46 and the second piston member 48 will be able to They are moved relative to each other in the axial direction thereof by a distance equal to the clearance S left between the radial end surface 68a and the engagement pawl 66a. However, in the present embodiment, the second engaging pawl 66b whose radially outer end portion is in abutting contact with the radial end face 68a axially biases the first piston member 46, thereby minimizing or preventing and the relative axial vibration movement between the second piston member 48.

The first shoulder 70 and the second shoulder 72 are located at different positions in the radial direction of the second piston member 48, and the radially inner ends of the first gap 74 and the second gap 76 are correspondingly located at different positions in the radial direction. at the location. In detail, the radially inner end portion of the first gap 74 is located slightly inside the inner peripheral surface of the cylindrical portion 46a of the first piston member 46 (in which the circumferential groove 51 is formed), and the diameter of the second gap 76 is The inner end is close to the inner circumference of the snap ring 50 and slightly outside the inner circumference of the snap ring 50 . Since the radially inner end portion of the first gap 74 is located slightly inside the inner peripheral surface of the first piston member 46, the snap ring 50 is applied from the peripheral portion of the second piston member 48 corresponding to the first engaging claw 66a. The amount of load is substantially equal to the amount of load applied to the snap ring 50 from the peripheral portion of the second piston member 48 not corresponding to the first engaging claw 66a and the second engaging claw 66b. Therefore, in the present embodiment, unlike the one in which the radially inner end portion of the first gap 74 is located close to or on the inner periphery of the snap ring 50 as is the radially inner end portion of the second gap 76 The load applied from the second piston member 48 to the snap ring 50 becomes more uniform in the circumferential direction of the snap ring 50 compared to the radially inner structure. The radial position of the radially inner end portion of the second gap 76 and the radial position of the second shoulder 72 are determined by the required elastic force to be generated by the second engaging pawl 66b, and can be located as shown in FIG. 5 . The outside of the radial position is sufficient as long as the elastic force to be generated is kept within a predetermined appropriate range.

In the radially outer piston 18 according to the present embodiment of the invention, the first gap 74 is formed between the first engaging claw 66a and the radially outer end portion of the snap ring 50, and the second gap 76 is formed between the second engaging claw 66a and the radially outer end portion of the snap ring 50. between the claw 66b and the snap ring 50, so that when the radially outer piston 18 moves axially to engage the clutch device 10 and applies an axial load from the second piston member 48 to the snap ring 50, the engagement claw 66 will not engage the snap ring 50. Ring 50 exerts force. Therefore, the radially outer piston 18 does not generate stress concentration at the peripheral portion of the circumferential groove 51 of the first piston member 46 adjacent to the axial notch 68, so that the thickness of the snap ring 50 can be made small.

Furthermore, the axial dimension d1 of the first gap 74 formed between the non-resiliently biased pawl in the form of the first engaging pawl 66a and the radially outer end portion of the snap ring 50 is smaller than the elastically biased pawl formed in the form of the second engaging pawl 66b. The axial dimension d2 of the second gap 76 between the biasing jaw and the snap ring 50 . This dimensional relationship between the first gap 74 and the second gap 76 is advantageous when assembling the first piston member 46 and the second piston member 48 . That is, the first engagement claw 66a and the second engagement claw 66b may be deformed due to the relative axial movement of the first piston member 46 and the second piston member 48 during assembly. Even in this deformation of the engaging claw 66 , the first engaging claw 66 a comes into abutting contact with the snap ring 50 before the second engaging claw 66 b comes into abutting contact with the snap ring 50 . When the first engaging pawl 66a is in abutting contact with the snap ring 50, further axial movement of the first piston member 46 relative to the second piston member 48 is prevented, thereby preventing subsequent elastic deformation of the second engaging pawl 66b, thereby preventing the first piston member 46 from being elastically deformed subsequently. The elastic deformation of the two engaging claws 66b enables the second engaging claws 66b to function as elastic biasing claws.

Referring now to Figure 6, there is shown a second piston member 82 of a piston according to a second embodiment of the present invention. The second piston part 82 has a plurality of first engaging claws 80 , one of which is shown in FIG. 6 . In this embodiment, each first engaging claw 80 is inclined at its proximal end away from the snap ring 50 in the axial direction of the second piston member 82 . The first engagement pawl 80 consists of a single straight portion extending radially toward the outside of the second piston member 82 and bent at its proximal end relative to the radial direction of the second piston member 82 so that The distal end of the single straight portion is spaced axially away from the snap ring 50 from its proximal end. No shoulder is provided for the first engaging pawl 80 because this first engaging pawl 80 does not comprise a radial portion parallel to the radial direction of the second piston member 82 . In this embodiment, too, a gap 84 is formed between each first engaging claw 80 and the radially outer end portion of the snap ring 50 . The first engagement pawl 80 is held in abutting contact with the radial end face 68a, and may be arranged to function as a resiliently biased pawl like the second engagement pawl 66b.

Referring now to Figure 7, there is shown a second piston member 48 of a piston according to a third embodiment of the present invention. The second piston member 48 in the third embodiment has the same constitution as that in the first embodiment shown in FIG. 4 except for the thickness of the engagement claw 66a. The engagement claw 66 a has a thickness smaller than other portions of the engagement claw 66 a and the second piston member 48 .

In the illustrated embodiment a radially outer piston is used for the clutch device 10, the principles of the invention are equally applicable to pistons for a brake device of an automatic transmission of a vehicle.

It should be understood that on the basis of the above disclosure, the present invention can be implemented by various other changes, alterations and improvements that can be conceived by those skilled in the art.

Claims (8)

1. A piston (18) for an automatic transmission, comprising: a first piston member (46) forming a cylindrical portion of the piston, formed with a plurality of axial slits (68) and a circumferential groove (51); a second piston member (48, 82) forming the bottom of the piston and having radially extending engagement jaws (66, 80) fitting in said axial cutouts; and a snap ring (50) fitted in said circumferential groove and held in abutting contact with said engagement pawl, whereby the first and second piston parts are fixed to each other, said piston being characterized in that: At least one of the plurality of engaging claws (66, 80) of the second piston member (48, 82) cooperates with the snap ring (50) to form a gap (74, 76, 84) therebetween. 2. Piston according to claim 1, characterized in that said at least one of said plurality of engagement jaws (66a, 66b) each has a shoulder (70) comprising a radially outer portion and a radially inner portion , 72), the radially outer portion and the radially inner portion are formed such that the radially outer portion is away from the snap ring (50) and the radially inner portion along the axial direction of the second piston member (48) The shoulders cooperate with the snap rings to form the gaps (74, 76). 3. Piston according to claim 1 or 2, characterized in that the axially inner ends of said plurality of axial cutouts (68) are defined by respective radial end faces (68a) which ) parallel to the radial direction of the first piston member (46) and along the axial direction of the first piston member away from the axially outer end of the axial notch and the circumferential groove (51) On, the plurality of engaging claws (66a, 66b) is composed of at least one elastically biased claw (66b) and at least one non-elastically biased claw (66a), wherein the at least one elastically biased claw (66b) is The axial direction of the second piston member (48) is inclined toward the radial end surface (68a) and each of the elastic biasing claws is in abutting contact with the radial end surface of a corresponding one of the plurality of axial slits. is kept, said at least one non-elastic biasing claw (66a) is not in abutting contact with the radial end face of the corresponding axial slit, each of said at least one non-elastic biasing claw (66a) is in contact with said snap ring (50) cooperate to define a first gap (74) therebetween, and each of said at least one resiliently biased pawl (66b) cooperates with said snap ring to define a second gap (76) therebetween, said first A dimension (d1) of the first gap in the axial direction of the piston (18) is smaller than a dimension (d2) of the second gap in the axial direction of the piston. 4. Piston according to claim 1 or 2, characterized in that said plurality of engagement jaws (66, 80) all cooperate with said snap ring (50) to form respective gaps (74, 76, 84) . 5. Piston according to claim 1 or 2, characterized in that each of said at least one of said plurality of engagement jaws (66a, 66b, 80) has a thickness equal to that of said second piston member (48, 82) The thickness of the remainder. 6. Piston according to claim 1 or 2, characterized in that the thickness of each of said at least one of said plurality of engagement jaws (66a, 66b, 80) is smaller than the thickness of the rest of said engagement jaws . 7. Piston according to claim 1 or 2, characterized in that said at least one of said plurality of engagement jaws (66a, 66b, 80) each consists of a single straight section, the single straight section part extends radially towards the outside of said second piston member (82) and is curved at its proximal end relative to the radial direction of the second piston member so that the distal end of the single straight portion runs along the is spaced axially away from the snap ring (50) from the proximal end. 8. Piston according to claim 1 or 2, characterized in that the inner end of the gap (74, 76, 84) is located at the The inner side of the inner peripheral surface of the first piston member (46).

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